Primary Protodolomite in Echinoid Skeletons

Schroeder, Johannes H.; Dwornik, E. J.; Papike, JJ

doi:10.1130/0016-7606(1969)80[1613:ppies]2.0.co;2

Cited by 89 publications

(64 citation statements)

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“…Some reports indicated that the magnesium contents change from place to place within the teeth (Schroeder et al 1969). We therefore examined the possibility that the magnesium contents differ within a single fibre.…”

Section: Results (A) Fibres : Key Structural Elementsmentioning

confidence: 99%

“…The magnesium carbonate content of the mineral in this part is as high as 43.5 mol % in L techinus ariegatus. This is the highest value found among natural magnesium-bearing calcites and is referred to as protodolomite (Schroeder et al 1969). Design strategies of sea urchin teeth R. Z. Wang and others Many morphological studies indicate that there are complex structural design strategies in sea urchin teeth, many of which are still not understood.…”

Section: Introductionmentioning

confidence: 99%

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Design strategies of sea urchin teeth: structure, composition and micromechanical relations to function

Wang

Addadi

Weiner

1997

Phil. Trans. R. Soc. Lond. B

168

177

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SUMMARYThe teeth of sea urchins comprise a variety of different structural entities, all of which are composed of magnesium-bearing calcite together with a small amount of organic material. The teeth are worn down continuously, but in such a way that they remain sharp and functional. Here we describe aspects of the structural, compositional and micromechanical properties of the teeth of Paracentrotus li idus using scanning electron microscopy, infrared spectrometry, atomic absorption, X-ray diffraction and microindentation. The S-shaped single crystalline calcitic fibres are one of the main structural elements of the tooth. They extend from the stone part to the keel. The diameter of the fibres increases gradually from less than 1 µm at the stone tip to about 20 µm at the keel end, while their MgCO $ contents decrease from about 13 mol % to about 4.5 mol %. Each fibre is coated by a thin organic sheath and surrounded by polycrystalline calcitic discs containing as much as 35 mol % MgCO $ . This structure constitutes a unique kind of gradient fibre-reinforced ceramic matrix composite, whose microhardness and toughness decrease gradually from the stone part to the keel. Primary plates are also important structural elements of the tooth. Each primary plate has a very unusual sandwich-like structure with a calcitic envelope surrounding a thin apparently amorphous CaCO $ layer. This central layer, together with the primary plate\disc interface, improves the toughness of this zone by stopping and blunting cracks. The selfsharpening function of the teeth is believed to result from the combination of the geometrical shape of the main structural elements and their spatial arrangement, the interfacial strength between structural elements, and the hardness gradient extending from the working stone part to the surrounding zones. The sea urchin tooth structure possesses an array of interesting functional design features, some of which may possibly be applicable to materials science.

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Section: Results (A) Fibres : Key Structural Elementsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Design strategies of sea urchin teeth: structure, composition and micromechanical relations to function

Wang

Addadi

Weiner

1997

Phil. Trans. R. Soc. Lond. B

168

177

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“…For example, the internal layer inside the plates is composed of ACC, and the cores of the needles are more soluble than their peripheries (7). The polycrystalline matrix crystals are so rich in Mg, that they were referred to as ''protodolomite,'' because the structure corresponds to disordered Mg calcite (12). Wang et al (7) showed that at least 75% of the Mg is located within the crystal lattice.…”

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confidence: 99%

“…The needle-plate complexes have been described as being all aligned such that a whole tooth behaves as a single crystal (5,12) based on X-ray diffraction, or as 2 crystals with a small angular offset based on polarized light microscopy (1-3); a dichotomy that is addressed in this study.…”

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confidence: 99%

The grinding tip of the sea urchin tooth exhibits exquisite control over calcite crystal orientation and Mg distribution

Aichmayer

Paris

et al. 2009

Proc. Natl. Acad. Sci. U.S.A.

162

157

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The sea urchin tooth is a remarkable grinding tool. Even though the tooth is composed almost entirely of calcite, it is used to grind holes into a rocky substrate itself often composed of calcite. Here, we use 3 complementary high-resolution tools to probe aspects of the structure of the grinding tip: X-ray photoelectron emission spectromicroscopy (X-PEEM), X-ray microdiffraction, and NanoSIMS. We confirm that the needles and plates are aligned and show here that even the high Mg polycrystalline matrix constituents are aligned with the other 2 structural elements when imaged at 20-nm resolution. Furthermore, we show that the entire tooth is composed of 2 cooriented polycrystalline blocks that differ in their orientations by only a few degrees. A unique feature of the grinding tip is that the structural elements from each coaligned block interdigitate. This interdigitation may influence the fracture process by creating a corrugated grinding surface. We also show that the overall Mg content of the tooth structural elements increases toward the grinding tip. This probably contributes to the increasing hardness of the tooth from the periphery to the tip. Clearly the formation of the tooth, and the tooth tip in particular, is amazingly well controlled. The improved understanding of these structural features could lead to the design of better mechanical grinding and cutting tools. echinoderms ͉ grinding tool ͉ self-sharpening ͉ spectromicroscopy ͉ X-ray microdiffraction

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“…High Mg 2þ /Ca 2þ -proportions (>4 : 1) for example lead to the formation of aragonite instead of calcite [2][3][4]. Aragonite usually does not include Mg 2þ , biogenic Mg-calcite crystals can incorporate up to 41 mol% Mg 2þ [5]. This integration of Mg 2þ into calcite is of huge importance regarding the properties and the use of these minerals [6].…”

Section: Introductionmentioning

confidence: 99%

Mixed calcium-magnesium pre-nucleation clusters enrich calcium

Verch

Antonietti

Cölfen

2012

Zeitschrift Für Kristallographie - Crystalline Materials

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Abstract. It is demonstrated that magnesium and carbonate ions can form pre-nucleation clusters in analogy to calcium carbonate. If a mixed calcium and magnesium solution is brought in contact with carbonate ions, mixed pre-nucleation clusters form. The equilibrium constants for their formation are reported revealing that over the entire range of possible cation mixing ratios, calcium gets enriched over magnesium in the pre-nucleation clusters. This can explain high magnesium contents in amorphous calcium carbonate. However, this enrichment alone is not sufficient to explain the magnesium content of less than 41 mol% which is found in magnesium calcite biominerals nucleated from seawater.

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Primary Protodolomite in Echinoid Skeletons

Cited by 89 publications

References 0 publications

Design strategies of sea urchin teeth: structure, composition and micromechanical relations to function

Design strategies of sea urchin teeth: structure, composition and micromechanical relations to function

The grinding tip of the sea urchin tooth exhibits exquisite control over calcite crystal orientation and Mg distribution

Mixed calcium-magnesium pre-nucleation clusters enrich calcium

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